Wind energy or wind power refers to the process by which the wind is used to generate mechanical power or electricity. Wind turbines convert the kinetic energy of the wind into mechanical power and that mechanical power is used to generate electricity. The generation of electricity by wind turbines is dependent on the strength of the wind at any given moment. Wind farm sites are chosen after careful analysis to determine the pattern of the wind regime, including its relative strength and direction at different times of the day and year.
In a conventional wind turbine, a large tower rests on a deep, solid foundation, supporting a nacelle with rotating blades at the top of the tower, the nacelle containing a gearbox, generator, power electronic devices, and yaw mechanism. The radius of the blades is large, as is the total weight carried by the tower. As a result, conventional wind turbines begin to produce power at wind speeds of about 4 m/s (9 mph) (i.e., the cut-in wind speed, or minimum wind speed needed to generate electricity), achieve rated power at approximately 12 m/s (29 mph), and stop power production at 25 m/s (56 mph). Examples of wind turbines are described in U.S. Pat. No. 8,729,721 (Borgen et al.), U.S. Pat. No. 8,721,258 (Ericksen et al.), and U.S. Pat. No. 8,669,672 (Stiesdal), all of which are incorporated herein by specific reference for all purposes.